Use of epiphyte plants as biomonitors to map atmospheric mercury in a gold trade center city, Amazon, Brazil

Evaluation of Hg in urban air is a quite complex and expensive task since conventional sampling systems are fragile and need special attention if long-term sampling is needed. Tillandsia usneoides, a Bromeliacea, is an epiphyte that captures all its nutrients from the atmosphere, and concomitantly accumulates heavy metals, among them mercury. Its morphology, with millimetric dimensions of the leaves and no roots, makes it ideal for handling and preparation of transplanting systems and due to its high relation between surface area and mass, has a high efficiency for Hg accumulation. One hundred systems of two baskets each with T. usneoides were distributed through Alta Floresta city—MT and recovered after an exposure of 15 and 45 days during the dry season (August–September, 1995) and also repeated during the rainy season (February–March, 1996). Each compartment (basket) contained 5 g of plants previously collected in a clean area. Only the younger parts were selected for transplantation experiments. Systems were hung at 2–20 m height in open areas, close to and in the surroundings of the gold shops as well as in control areas. Relative occupational exposure was also evaluated with systems installed inside gold dealer shops. Concentrations of Hg in the exposed plants were remarkably high in the shops, reaching values up to 26 ppm (parts per million) or 300 times higher than in the control plants.